Mobile electrical substations (also known as “mobiles”) may be used in place of distribution or transmission substations (e.g., in emergency situations, or for maintenance/construction purposes, etc.). The use of such mobile electrical substations involves certain challenges such as dimensional and weight restrictions. More specifically, such mobile electrical substations are transported on roads, where local and federal codes define limits in regard to weight and dimensions. In the technical specifications, the design of such mobile electrical substations is driven largely by power (e.g., MVA) and the voltage level (e.g., kV). In regard to dimensions, height is a key concern. There are two main modes for a mobile electrical substation: transport mode; and operational mode. In transport mode, the mobile electrical substation is configured to meet the imposed dimensional road limits. During operational mode, the spacing between some components (e.g., the switchgear in a three phase mobile substation) is increased for dielectric distance requirements due to high voltage. A critical part of this change between the transport mode and the operational mode is the racking mechanism. The racking mechanism moves components of the mobile electrical substation (e.g., high voltage switchgear components) into the configuration desired for the operational mode.
There are different types of conventional racking mechanisms in use. They can mainly be categorized into a draw out style, and a pivoting style. Both of these styles use three main components: (1) a movable structural member; (2) a fixed structural member; and (3) bearings to enable the movable structural member to assume different positions between the transport mode and the operational mode. The pivoting style (which is often used for higher kV applications) has complex features, and presents challenges in the design of the pivoting point and fixture into the desired position. The draw out style (illustrated in FIG. 11) usually employs bearings below and above the movable structural member, such that the fixed structural member envelops the moveable structural member and the bearings. FIG. 11 illustrates an example of a prior art racking system 10 including: first support platform 12 engaged with first moveable member 12a which moves with respect to first fixed member 12b; stationary platform 14; and second support platform 16 engaged with second moveable member 16a which moves with respect to second fixed member 16b. A relatively large number of bearings 16c are provided above and below the respective moveable members (e.g., moveable member 16a), resulting in the challenges recited herein.
Due to constraints in the height of the mobile electrical substation, smaller bearings are often utilized, thereby resulting in a higher number of bearings being used. The bearings are usually directly mounted to the enveloping fixed structural member involving special, high precision threads. Due to the complexity, and the amount of material used, certain of the components are often formed from a lighter, but more expensive, material such as aluminum. This adds further complexity to the design.
Thus, it would be desirable to provide improved racking mechanisms for mobile electrical substations overcoming one or more of the deficiencies of conventional racking mechanisms.